Mechanical diesel engine fuel injectors of the type to which the invention relates have a housing which may include a body assembly block in or to which other parts of the injector housing and various other elements of the unit injector are directly or indirectly mounted. Typically, the follower projects upward from the top of the injector body and has a working face at its top end. The injector housing may include an elongated hollow housing nut threaded on a boss extending from the bottom of the body assembly block. Mounted in the housing are the pump plunger, a bushing for the plunger, a check valve, and other elements. At the lower end is a spray tip. The housing nut may contain and clamp many of the housed elements in assembled stacked relation below the body assembly block.
Information pertaining to the fuel injector is marked on the flat front face of the body assembly block. The markings or indicia, usually in the form of alpha-numeric characters, are stamped on with individual steel dies (one for each character) that incise the characters into the face. The face is finished with a machined surface on which the incised characters are visible. The information can be stamped in ink, but ink markings are generally unsatisfactory because they can rub off or fade so that the information they contain is lost.
The stamped-on information includes information important to the long-term economic use of the injector. Such information includes information uniquely specific to the injector that is being marked, such as a unique serial number for each one of a series of injectors. (The same part number would apply to each member of the series, but each member would have its own unique serial number.) The information may include, directly or in coded key, manufacturer, year and month of manufacture, customer prefix and suffix numbers, part number, serial number, and warranty expiration date.
In many applications it is hard to see even the front face of an installed fuel injector, because the injector is installed in the engine cylinder head and the engine is installed in the engine compartment of a locomotive or other vehicle in such a way as to prevent directly observing the face. In order to obtain information marked on an injector, it may be necessary to remove the injector from the engine and then reinstall it again if its use is to be continued. Sometimes the marking can be read by using mirrors and lights, but that is also inconvenient and bothersome.
Injectors of the type to which the invention relates are remanufactured from time to time. This work may be done either by the original manufacturer or by other companies specializing in rebuilding. Railroads and truck lines, for example, have injectors rebuilt as a routine operating practice, just as truck lines have tires retreaded as a routine operating practice.
When an injector is remanufactured, the information to be marked on it must be updated. Generally, the available area for stamping information on the front face is limited, and the old information must be removed to make room for updated information, and also to eliminate any potential for confusion between old and new information. The practice is to machine or grind the flat front face to a depth sufficient to erase all the old markings and then stamp the new set of information items on the freshly exposed "new" surface of the front face. After this has been done several times, the body assembly block falls short of specified dimensional tolerances and must be replaced. Since the body assembly block is a major component of the overall injector assembly, the requirement that the block be replaced say every two or three rebuilding cycles represents a significant cost factor.
During operation of the injector, the upwardly-projecting follower is forced straight downward by a cam-driven rocker-arm linkage which engages the follower at the working face or top face of the follower. The follower spring returns the follower straight upward as permitted by the contour of the cam which drives the rocker arm. The rocker-arm element that engages the follower moves with a rocking motion rather than moving straight up and down. Therefore there is a slight relative sideways motion between the power output end of the rocker arm and the working face of the follower as the follower advances and returns.
This relative sideways motion is accommodated by a sliding action between the working face of the follower and the rocker-arm element that engages the follower face. Thus the parts transmit the high forces required to longitudinally advance the injector plunger while at the same time the part slide relative to each other along a direction transverse to tile longitudinal path of plunger advance. The working face is hardened by heat treating to better resist wear under the stressful conditions presented by such combination of high longitudinal force transmission and transverse relative sliding action.
In order to distribute and minimize compressive stresses and wear, the power output end of the rocker arm is provided with a ball-and-socket type swivel pad or shoe having a flat bottom face that is in face-to-face contact with the hardened working face of the follower. The flat face of the shoe slides back and forth sideways through a short distance across the flat working face of the follower as the rocker arm drives the follower downward and as the return spring lifts it upward. This face-to-face working contact avoids the occurrence of the extremely high local stresses that would be experienced if the contact between the working face of the follower and the element serving as the power output end of the rocker-arm linkage were point contact or line contact rather than face-to-face contact.